I have a metro mini that has inputs and outputs soldered to most of the pins (not d0 or d1 though). When I plug it in to my computer with a micro usb, the red led flashes really quickly (three times I think) and then turns off. The power led remains solidly on. The board then does not show up in the arduino ide as being connected to a port. Is this just a faulty board? Or is there a possibility that this is caused by something connected to the pins? None of the inputs are powered separately--they all are powered by the metro itself.

If this is an escape room, and something where someone is paying (you, or for the experience), it should be a bit more bulletproofIt is easier to debugIt is easier to swap out a new Metro, in case you blow that one upIn case you need to change code and you aren't around, you can program one, and send it via UPS/Fedex, and say, "replace this!"

You could go the further step and connectorize everything with polarized connectors, so you can debug this on the fly. When soldered up, it is difficult to debug, since you have an all-or-nothing situation.

Tough to see where you might have shorted something out from the pictures. it may be the issue is not at your soldering on the Metro Mini, but on the connections on the other end.

As a sanity check, verify your USB cable by using it to connect some other, known-working device to a computer.

There's a plague of charge-only cables out there with USB connectors at both ends, but no wires for the data signals. We see people get caught by them every day.

Just changing cables doesn't work. It's become normal for people to say they had to try three or four cables before finding one that worked, and IIRC, the record is 10. You need the true positive of a working connection to rule out the false negative of a charge-only cable.